ceph/src/boost/libs/hana/include/boost/hana/or.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::or_`.
   4
   5 @copyright Louis Dionne 2013-2016
   6 Distributed under the Boost Software License, Version 1.0.
   7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   8  */
   9
  10 #ifndef BOOST_HANA_OR_HPP
  11 #define BOOST_HANA_OR_HPP
  12
  13 #include <boost/hana/fwd/or.hpp>
  14
  15 #include <boost/hana/concept/logical.hpp>
  16 #include <boost/hana/config.hpp>
  17 #include <boost/hana/core/dispatch.hpp>
  18 #include <boost/hana/detail/variadic/foldl1.hpp>
  19 #include <boost/hana/if.hpp>
  20
  21
  22 BOOST_HANA_NAMESPACE_BEGIN
  23     //! @cond
  24     template <typename X, typename Y>
  25     constexpr decltype(auto) or_t::operator()(X&& x, Y&& y) const {
  26         using Bool = typename hana::tag_of<X>::type;
  27         using Or = BOOST_HANA_DISPATCH_IF(or_impl<Bool>,
  28             hana::Logical<Bool>::value
  29         );
  30
  31     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  32         static_assert(hana::Logical<Bool>::value,
  33         "hana::or_(x, y) requires 'x' to be a Logical");
  34     #endif
  35
  36         return Or::apply(static_cast<X&&>(x), static_cast<Y&&>(y));
  37     }
  38
  39     template <typename X, typename ...Y>
  40     constexpr decltype(auto) or_t::operator()(X&& x, Y&& ...y) const {
  41         return detail::variadic::foldl1(
  42             *this,
  43             static_cast<X&&>(x),
  44             static_cast<Y&&>(y)...
  45         );
  46     }
  47     //! @endcond
  48
  49     template <typename L, bool condition>
  50     struct or_impl<L, when<condition>> : hana::default_ {
  51         template <typename X, typename Y>
  52         static constexpr decltype(auto) apply(X&& x, Y&& y) {
  53             //! @todo How to forward `x` here? Since the arguments to `if_`
  54             //! can be evaluated in any order, we have to be careful not to
  55             //! use `x` in a moved-from state.
  56             return hana::if_(x, x, static_cast<Y&&>(y));
  57         }
  58     };
  59 BOOST_HANA_NAMESPACE_END
  60
  61 #endif // !BOOST_HANA_OR_HPP